This invention relates to a configuration of the transmission lines of a ring network, and more particularly to a ring network configuration in active wiring concetrators (or line concentrators) for improving the reliability of signal transmission over the transmission lines.
A method disclosed in, for example, "Local Area Network According to Token Ring Access Method", Bit Magazine, Vol. 16, No. 3, 1984 is known as one of prior art methods relating to a transmission line configuration for accommodating a plurality of line concentrators in a ring network. The prior art method of this kind is such that, when a failure occurs on a ring segment connection between line concentrators (which are called active wiring concentrators (AWC) in the publication), the line concentrator located downstream of the defective ring segment connects a backup ring to a lobe extending toward the main ring, thereby interrupting the flow of a timing signal through the backup ring. The line concentrator located on the downstream side of the backup ring recognizes the disappearance of the backup ring segment and changes the connection of the main ring, thereby re-arranging the ring network. However, the state of the disconnected transmission line is not sufficiently considered in the prior art method described above. For example, when the transmission line is disconnected at a line concentrator located on the upstream side of the backup ring segment corresponding to the disconnected transmission line, sufficient consideration is not given to the problem of signal reflection and crosstalk, which have to be decreased, occurring in the line between the line concentrators located on the upstream and downstream sides of the backup ring.
As another prior art, a method disclosed in "IEEE 802.5R Draft G Vo. 6, Draft Document on Reconfiguration Draft Version G-8 Sept. 86" is known. According to this prior art method, a signal detector (referred to hereinafter as an SD) is inserted in a signal receiving ring of a ring pair so as to monitor a signal transmitted through the signal transmission line. However, the publication describes nothing as to connection and disconnection between the transmission line and the SD connected to the transmission line.
As discussed above, sufficient consideration is not given in the former prior art method as to the need of decreasing the signal reflection and crosstalk in the transmission line in the event of disconnection of the transmission line. Also, in the case of the latter prior art method in which the SD is kept connected to the transmission line under the normal operating condition of the ring network, a loss tends to occur in the signal being transmitted through the transmission line, resulting in a lowered reliability of signal transmission over the ring transmission line.